Hydrocarbon leak detection cable

ABSTRACT

Disclosed are embodiments of hydrocarbon leak detection cables that utilize time domain reflectometry to indicate the location of changes in impedance in a hydrocarbon leak detection cable. In addition, an embodiment of a hydrocarbon leak detection optical fiber is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. § 120 as a divisional of U.S. Utility application Ser. No.17/235,156, entitled, “HYDROCARBON LEAK DETECTION CABLE,” filed on Apr.20, 2021 and is incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes.

BACKGROUND

Monitoring of leaks of hydrocarbons such as oil, gas, and otherpetroleum fluids is important in protecting the environment. Hydrocarbonleaks can occur from both underground and above ground storage tanks,pipelines, petroleum fluid transfer pipes and tubing and machinery thatruns on petroleum fluids, such as diesel generators, etc. Leaks cancontaminate the ground water table which can cause serious harm to ageographical area. Detection of leaks prior to contaminations byhydrocarbons and petroleum fluids is therefore advantageous andimportant in the oil and gas industry.

SUMMARY

An embodiment of the present invention may therefore comprise: a methodof detecting hydrocarbon leaks using a hydrocarbon leak detection cablecomprising: providing a hydrocarbon leak detection cable having ahydrocarbon reactive polymer that expands in the presence ofhydrocarbons and generates forces that move a conductive sheath closerto a center conductor of the hydrocarbon leak detection cable whichchanges impedance of the hydrocarbon leak detection cable at a locationwhere the hydrocarbons are contacting the hydrocarbon leak detectioncable; using a time domain reflectometer to detect the location on thehydrocarbon leak detection cable.

An embodiment of the present invention may further comprise: a method ofdetecting a location of a hydrocarbon leak in a hydrocarbon leakdetection cable comprising: using a layer of hydrocarbon reactivepolymer that functions as an electrical shield in the hydrocarbon leakdetection cable, and that surrounds a center conductor at apredetermined distance which creates a predetermined input impedance ofthe hydrocarbon leak detection cable, the hydrocarbon reactive polymerhaving conductive particles dispersed in the hydrocarbon reactivepolymer which causes the hydrocarbon reactive polymer to be conductiveand function as an electrical shield; detecting a hydrocarbon leak atthe location on the hydrocarbon leak detection cable by allowing liquidhydrocarbon from the hydrocarbon leak to penetrate the hydrocarbon leakdetection cable at the location causing the hydrocarbon reactive polymerto absorb the liquid hydrocarbon, which causes the hydrocarbon reactivepolymer to swell so that the conductive particles move away from eachother thereby reducing conductivity of the layer of hydrocarbon reactivepolymer and causing the hydrocarbon leak detection cable to changeimpedance at the location; using a time domain reflectometer todetermine where on the hydrocarbon leak detection cable the change ofimpedance has occurred to determine the location of the hydrocarbonleak.

An embodiment of the present invention may further comprise: a method ofdetecting a hydrocarbon leak comprising: providing a hydrocarbon leakdetection cable having a hydrocarbon reactive polymer that expands whenplaced in contact with liquid hydrocarbons and generates forces thatmove a conductive sheath away from a center conductor in the hydrocarbonleak detection cable, causing a change in impedance of the hydrocarbonleak detection cable at a location where the liquid hydrocarbons contactthe hydrocarbon leak detection cable; using a time domain reflectometerto detect the location on the hydrocarbon leak detection cable.

An embodiment of the present invention may further comprise: a method ofdetecting a hydrocarbon leak comprising: providing a hydrocarbon leakdetection optical cable having a hydrocarbon reactive polymer thatcreates a reflective interface with a fiber optic filament to reflectlight that is transmitted through the fiber optic filament, thereflective interface being altered when liquid hydrocarbons contact thehydrocarbon reactive polymer, causing the reflective interface toscatter light; detecting the scattered light to determine a location ofthe hydrocarbon leak.

An embodiment of the present invention may further comprise: a method ofdetecting a hydrocarbon leak comprising: providing a hydrocarbon leakdetection optical cable having a hydrocarbon permeable cladding thatcreates a reflective interface with a fiber optic filament to reflectlight that is transmitted through the fiber optic filament, thereflective interface being altered when liquid hydrocarbons contact thereflective interface, causing the reflective interface to scatter light;detecting the scattered light to determine a location of the hydrocarbonleak.

An embodiment of the present invention may further comprise: a method ofdetecting a hydrocarbon leak comprising: providing a hydrocarbon leakdetection cable having a shaped dielectric that covers a centerconductor, and a hydrocarbon permeable membrane that covers the shapeddielectric and forms spaces between the shaped dielectric and thehydrocarbon permeable membrane, and a hydrocarbon permeable conductivesheath that covers the hydrocarbon permeable membrane which provides aconductive shield for the center conductor which creates a predeterminedinput impedance of the hydrocarbon leak detection cable, the hydrocarbonpermeable membrane and the hydrocarbon permeable conductive sheathallowing liquid hydrocarbons from a hydrocarbon leak to penetrate thehydrocarbon permeable membrane and the hydrocarbon permeable conductivesheath and collect in the spaces between the shaped dielectric and thehydrocarbon permeable membrane which changes impedance of thehydrocarbon leak detection cable at a location where the liquidhydrocarbons penetrate the hydrocarbon permeable membrane and thehydrocarbon permeable conductive sheath; using a time domainreflectometer to detect the location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cut-away view of an embodiment of a hydrocarbondetection cable.

FIG. 2 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable of FIG. 1 .

FIG. 3 is a partial cut-away view of another embodiment of thehydrocarbon detection cable.

FIG. 4 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable of FIG. 3 .

FIG. 5 is a partial cut-away view of another embodiment of thehydrocarbon leak detection cable.

FIG. 6 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable of FIG. 5 .

FIG. 7 is a partial cut-away view of a hydrocarbon leak detectionoptical fiber.

FIG. 8 is a cross-sectional view of the embodiment of the hydrocarbonleak detection optical fiber of FIG. 7 .

FIG. 9 is a partial cut-away view of another embodiment of thehydrocarbon leak detection cable.

FIG. 10 is a cross-sectional view of the hydrocarbon leak detectioncable of FIG. 9 .

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a partial cut-away view of an embodiment of a hydrocarbon leakdetection cable 100. As illustrated in FIG. 1 the hydrocarbon leakdetection cable 100 has an outer non-expandable permeable cover 102. Thenon-expandable permeable cover 102 is intended to protect thehydrocarbon leak detection cable 100 from abrasions, punctures and otherpotential damage. The non-expandable permeable cover 102 may beconstructed from a plastic monofilament fiber that is braided in amanner that provides protection to the underlying layers. Themonofilament fiber can be constructed from various plastics, andnormally has a coverage of approximately 80%, so that 20% of the surfaceof the non-expandable permeable cover 102 is open to allow the passageof various liquids including hydrocarbons. Of course, those percentagescan be used including 90/10, 70/30, for example. The non-expandablepermeable cover 102 may also be made from various types of polymer tapehaving perforations to allow the passage of a liquid such as liquidhydrocarbons. Various other types of materials can be used to producethe non-expandable permeable cover 102 which does not allow substantialexpansion as a result of forces created by the hydrocarbon reactivepolymer layer 104. In the regard, substantial expansion means that thenon-expandable permeable cover 102 expands by more than about 10% of itsdiameter.

Under the non-expandable permeable cover 102, illustrated in FIG. 1 , isa hydrocarbon reactive polymer 104. In that regard, each of the layersor coverings illustrated in all of the embodiments may includeadditional layers. So, for example, in FIG. 1 , there are four differentlayers illustrated that surround or cover the center conductor 110.However, other additional layers may exist, and it should be understoodby those skilled in the art that the description provided herein, andthe claims set forth, a structure which may include additional layers orcoverings. Terms such as “under,” “cover,” “on,” “surrounds” and similarterms do not mean that any particular layer is directly connected to ordirectly adjacent to any other layer, but rather, other layers can existin the structures in the embodiments disclosed. Further, these terms donot mean or imply “complete,” but may be “partial.”

Referring again to FIG. 1 , hydrocarbons that pass through thenon-expandable permeable cover 102 react with the hydrocarbon reactivepolymer 104 which expands or swells when subjected to, or placed incontact with, hydrocarbons. The hydrocarbon reactive polymer 104 maycomprise a petroleum fluid gel which absorbs hydrocarbons and is basedupon polyolefin polymers. Polyolefin-based hydrophobic absorbancedemonstrates selective absorption of hydrocarbon molecules in watersolutions. This is more fully disclosed in a publication of the AmericanChemical Society relating to “Macromolecules” entitled “Petro gel: NewHydrocarbon (oil) Absorbent Based on Polyolefin Polymers” by ChangwloNam, Houxiang Li, Gang Zhang, and T. C. Mike Chung, Department ofMaterial Science and Engineering, the Pennsylvania State University,University Park, Pennsylvania 16802. In general, various rubber andnitrile-based materials are capable of absorbing hydrocarbons and swellin three dimensions as a result of the absorption of the hydrocarbons.These polymers absorb the hydrocarbon liquid and swell which creates areactive force on the non-expandable permeable cover 102 so that theforces created by the swelling are all directed inwardly towards theconductive sheath 106.

The conductive sheath 106, illustrated in FIG. 1 , can be made ofstainless steel, copper, a conductive polymer coated mesh, tin platedcopper or any type of conductive material that may function as a shield.The term “sheath” is used to mean a protective covering around anelectrical cable. The term “sheath” is synonymous with the term “shield”as used in shielded cables since conductive sheaths, as used herein,such as conductive sheath 106, provides shielding to a surrounded centerconductor such as center conductor 110. The conductive sheaths disclosedherein provide shielding such as provided by a Faraday cage and alsoprovide a conductive path that extends along the cable for detectingmultiple leaks. The conductive sheath 106 provides shielding so that thehydrocarbon leak detection cable 100 has a preset or predetermined inputimpedance. For example, the hydrocarbon leak detection cable 100 mayhave a 50 ohm input impedance which is determined by the spacing betweenthe conductive sheath 106 and the center conductor 110. This spacing isalso affected by the material used for the low loss, low dielectriccompressible material 108. The amount of spacing between the conductivesheath 106 and the center conductor 110, to achieve a particular inputimpedance, is dependent upon the dielectric constant of the low loss,low dielectric compressible material 108. For example, various materialscan be used for the low loss, low dielectric compressible material 108,such as a silicon, rubber foam, any polymer-based foams or othercompressible material. Since air has a dielectric constant of one, afoam material provides a large amount of air which will create a lowdielectric constant for the low loss, low dielectric compressiblematerial 108. Of course, the lower the dielectric constant of the lowloss, low dielectric material 108, the less spacing is required betweenthe center conductor 110 and the conductive sheath 106 to obtain thedesired impedance. The center conductor 110, of course can be made ofany conductive material such as copper or other wire or conductivematerial.

The hydrocarbon leak detection cable 100 may be placed in locations thatare difficult to access in order to detect hydrocarbon leaks. Thehydrocarbon leak detection cable 100 may be placed in a perforated pipethat can be disposed in various locations, such as under above groundtanks, under below ground tanks, under a pipeline that rests in sand,etc. The hydrocarbon leak detection cable 100 may also be placed in acontainment pipe of a double wall pipeline or transmission pipe, in acontainment tank located under an underground tank and other locationsthat are difficult to access. It is therefore advantageous to be able toreuse the hydrocarbon leak detection cable 100. In that regard, thehydrocarbon leak detection cable 100 can be dried out after ahydrocarbon leak has been sealed so that the hydrocarbon reactivepolymer 104 returns to its normal size prior to absorption ofhydrocarbons. In that case, the low loss, low dielectric compressiblematerial 108 should be made from a material that can return to itsoriginal size after being compressed. Many rubbers and synthetic foamsincluding silicon foams are capable being compressed and then expandingto an original size after being compressed.

In addition, the hydrocarbon leak detection cable 100 can be cleanedusing various methods to remove hydrocarbons. For example, varioussolvents and soaps, including isopropyl alcohol, glycerin, propyleneglycol have been used to remove the hydrocarbons.

Alternatively, materials can be used that do not return to their normalsize prior to absorption of hydrocarbons and as such, the cable cansimply be replaced. In many applications, this simply requires cablepulling to replace the cable with a new cable. These types of cables maybe less expensive to implement and may be more reliable since somematerials simply do not return fully to their pre-expanded size. Assuch, the embodiments disclosed herein, as well as the claims may referto the use of materials that may be either reusable or may not bereusable and require replacement.

In many applications, the hydrocarbon leak detection cable 100 may belaid out over a long distance to locate the position of any leak. Forexample, the hydrocarbon leak detection cable 100 can be used to locatethe position of a leak in a long pipeline. Similarly, if there is alarge underground tank, the hydrocarbon leak detection cable 100 can beused to locate the position of the leak with regard to the tank so thatthe location of excavation around the tank can be determined for sealingleaks.

The location of the leak on a leak detection cable can be determined byusing time domain reflectometry (TDR). TDR uses the concept of measuringreflections along a conductor. A time domain reflectometer generates aninterrogation pulse that is transmitted along the conductor. A change inimpedance along the conductor will create a reflected wave in theconductor. As long as the conductor has a substantially uniformimpedance along its length, such as 50 ohms, and is properly terminated,then no reflections will be detected, and the interrogation pulsegenerated by the time domain reflectometer is absorbed at the far end byproper termination of the cable. If there is an impedance variationsomewhere along the cable, the pulse will be reflected back to thesource. The location of the reflection, and the change in impedance, onthe cable is easily determined by measuring the time lapse between thegeneration of the interrogation pulse and the reception of the reflectedsignal.

FIG. 2 is a cross-section view of the hydrocarbon leak detection cable100 illustrated in FIG. 1 . As illustrated in FIG. 2 , thenon-expandable permeable cover 102 surrounds the hydrocarbon leakdetection cable 100. The non-expandable permeable cover 102 allowshydrocarbons to seep through the non-expandable permeable cover 102 andcontact the hydrocarbon reactive polymer layer 104. The hydrocarbonreactive polymer 104 functions to swell or expand when the hydrocarbonreactive polymer 104 absorbs hydrocarbons allowed to pass through thenon-expandable permeable cover 102. The non-expandable permeable cover102 directs the forces of the expansion of the hydrocarbon reactivepolymer 104 in an inward direction to compress the conductive sheath 106inwardly. The forces on the conductive sheath 106 cause the low loss,low dielectric compressible material 108 to compress so that theconductive sheath 106 moves closer to the center conductor 110. When theconductive sheath 106 moves closer to the center conductor 110, theimpedance of the hydrocarbon leak detection cable 100 changes at thelocation where the hydrocarbon has penetrated the hydrocarbon leakdetection cable 100. The change in impedance of the hydrocarbon leakdetection cable 100 at that location causes a reflection of aninterrogation pulse wave generated by a time domain reflectometer sothat a reflected wave is transmitted back towards the origin of theinterrogation pulse wave. A time domain reflectometer detects thereflected pulse wave and measures the time between the generation of theinterrogation pulse and the reception of the reflected pulse. Thatelapsed time is an indication of a location of the change of impedancein the hydrocarbon leak detection cable 100 so that the location of thehydrocarbon leak can be determined.

FIG. 3 is a schematic cut-away view of another embodiment of ahydrocarbon leak detection cable 300. As illustrated in FIG. 3 , thehydrocarbon leak detection cable 300 has an outer expandable, permeableprotective outer cover 302. The expandable, permeable protective outercover 302 may be made from expandable materials that can expand and thencontract to their original size. Non-contracting outer covers can alsobe used. The expandable, permeable protective outer cover 302 is alsopermeable to liquid hydrocarbons which can seep through the expandable,permeable protective outer cover 302 and penetrate the hydrocarbonreactive polymer 304, which contains carbon nanotubes and/or conductiveparticles such as carbon particles or other conductive particles orelements. The expandable, permeable protective outer cover 302 providesprotection against punctures and is wear resistant. The expandable,permeable protective outer cover 302 also may be made from a conductivematerial that provides conduction throughout the length of thehydrocarbon leak detection cable 300, even though a local leak has beendetected. The conduction can be provided by a conductive coating ofvarious expandable materials, or simply by providing an expandable wirebraid, such as a copper wire braid, as part of the expandable, permeableprotective outer cover 302, or as a separate inner layer. Using aconductive expandable, permeable protective outer cover 302 allowsconduction along the length of the cable 300 so that multiple leaks canbe detected along the length of cable 300.

The hydrocarbon reactive polymer 304, illustrated in FIG. 3 , may havecarbon-nanotubes and/or carbon particles or other conductive particlesor conductive elements dispersed throughout the polymer material so thatthe hydrocarbon reactive polymer 304 is conductive and creates aconductive shield for the hydrocarbon leak detection cable 300. Theimpedance of the hydrocarbon leak detection cable 300 is created by thespacing between the hydrocarbon reactive polymer 304, which acts as aconductive shield, and the center conductor 308. Low loss, lowdielectric non-compressible material 306 is disposed between thehydrocarbon reactive polymer layer 304 and the center conductor 308.Depending upon the dielectric constant of the low loss, low dielectricnon-compressible material 306, and the spacing between the hydrocarbonreactive polymer 304 and the center conductor 308, the input impedanceof the hydrocarbon leak detection cable 300 can be established. In otherwords, the low loss, low dielectric non-compressible material 306 mayhave a higher dielectric constant which will require that the low loss,low dielectric non-compressible material 306 be thicker than thecompressible foam layer 108 illustrated in FIGS. 1 and 2 . In order tomaintain an input impedance of 50 ohms for the hydrocarbon leakdetection cable 300, a thicker layer of non-compressible material may berequired. The low loss, low dielectric non-compressible material 306, aswell as other low loss, low dielectric non-compressible materialsdisclosed in other embodiments, can comprise compressible materials thatmay compress in response to hydrocarbon reactive polymers, such ashydrocarbon reactive polymer 304, until they simply do not compress anyfarther so that the hydrocarbon reactive polymer 304 expands outwardlycreating spacing between the carbon nano-tubes, carbon particles orother conductive particle or conductive elements which creates a lowerconductance. Since the input impedance of the cable is maintained at apre-determined input impedance such as 50 ohms, very low dielectricmaterials such as foams that contain high percentage of air can be madethinner and still maintain the 50 ohm impedance. These types of highratio air foams are very compressible but are thinner than otherdielectric materials and can be compressed by a lesser amount until theyare no longer compressible. These types of foams and other compressiblematerials may be suitable as a replacement for the low loss, lowdielectric non-compressible material 306, as long as there is asufficient amount of the hydrocarbon reactive polymer 304 to cause thelow loss, low dielectric non-compressible material 306 to compress untillayer 306 can compress no more, so that the hydrocarbon reactive polymerlayer 304 continues to expand and create a lower conductance or loss ofconductance. The same is also true for the low loss, low dielectricnon-compressible material 506 of FIG. 5 , as disclosed below.

When liquid hydrocarbons penetrate the expandable, permeable protectiveouter cover 302 and are absorbed by the hydrocarbon reactive polymerlayer 304, as illustrated in FIG. 3 , the hydrocarbon reactive polymerlayer 304 expands outwardly, since the expandable, permeable protectiveouter cover 302 is expandable and the low loss, low dielectricnon-compressible material 306 is non-compressible. The expansion of thehydrocarbon reactive polymer 304 causes the nanotubes and/or carbonparticles in the hydrocarbon reactive polymer 304 to separate whichlowers the conductivity of the hydrocarbon reactive polymer layer 304.In some cases, and depending upon the concentration of the carbonnanotubes and/or carbon particles in the hydrocarbon reactive polymerlayer 304, the hydrocarbon reactive polymer layer 304 may expandsufficiently to cause the hydrocarbon reactive polymer layer 304 to haveless conductivity or become non-conductive at the location where thehydrocarbons have penetrated the expandable, permeable protective outercover 302 and have been absorbed by the hydrocarbon reactive polymer304. A lower conductivity or loss of conductivity of the hydrocarbonreactive polymer 304 causes a change in impedance between the centerconductor 308 and the hydrocarbon reactive polymer 304. A change inimpedance can then be detected and the location of that change ofimpedance on the cable can be determined using a time domainreflectometer, as described above.

In an alternative embodiment, the expandable, permeable protective outercover 302 can be eliminated. In this embodiment, the hydrocarbonreactive polymer 304 can be made sufficiently durable so that anexpandable, permeable protective outer cover 302 is not needed. Polymerlayers can be constructed of polymers that are sufficiently durable towithstand the wear and tear that a cable may be subjected to duringinstallation and use.

FIG. 4 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable 300 illustrated in FIG. 3 . As illustrated in FIG.4 , the hydrocarbon leak detection cable 300 has an expandable,permeable protective outer cover 302 which surrounds a hydrocarbonreactive polymer layer 304 having carbon nanotubes and/or carbon fibers.A low loss, low dielectric non-compressible material 306 surrounds acenter conductor 308. The low loss, low dielectric non-compressiblematerial 306 may be a Teflon based polymer, polyethylene, or an acrylicsuch as LDPE, PTFE, PEEK, PFN and many others. Other low loss polymerssuch as HDPE, hard rubber, silicon, etc. may be sufficiently dense andhave a sufficiently low dielectric and low loss characteristics to beused for the low loss, low dielectric non-compressible material 306. Thedriving factors in determining the selection of the low loss, lowdielectric non-compressible material 306 are that the material is costeffective and it can function as a low loss dielectric. In addition,with regard to the embodiment of FIG. 1 , the low loss dielectric mustbe compressible. With regard to the embodiments of FIGS. 3 and 4 , thelow loss dielectric must be substantially non-compressible, i.e., havinga compressibility of less than 10% with respect to the forces created bythe hydrocarbon reactive polymer 304 in the hydrocarbon leak detectioncable 300. As such, the term “non-compressible” as used throughout thisdisclosure, and in the claims, is not an absolute term and somecompression can occur. Again, compression less than 10% of the diameterof a “non-compressible” material is allowable.

FIG. 5 is another embodiment of a hydrocarbon leak detection cable 500.As illustrated in FIG. 5 , the hydrocarbon leak detection cable 500 hasan expandable, permeable conductive cover 502. The expandable, permeableconductive cover 502 can be constructed in the same manner as theexpandable, permeable protective outer cover 302 of FIG. 3 to provide aprotective, permeable cover that is abrasion resistant and capable ofprotecting the hydrocarbon leak detection cable 500. In an alternativeembodiment, the expandable, permeable conductive cover 502 can beeliminated. As such, the hydrocarbon reactive polymer 504 can be madesufficiently durable so that an expandable, permeable conductive cover502 is not needed. Polymer layers and conductive sheath 503 can beconstructed of materials that are sufficiently durable to withstand thewear and tear that a cable may be subjected to during installation anduse. Under the expandable, permeable conductive cover 502, when present,is a conductive sheath 503. The conductive sheath 503 may be constructedfrom materials that allow the conductive sheath 503 to expand, such as aloosely wound wire braid, other conductive braid, or a conductive,expandable tape having perforations or other materials. An expandable,porous polymer material that is coated with or mixed with a conductivematerial, such as carbon particles or carbon nanoparticles, can also beused. The hydrocarbon reactive polymer 504 absorbs hydrocarbons that aretransmitted through the expandable, permeable conductive cover 502 andthe conductive sheath 503. As the hydrocarbon reactive polymer 504absorbs the hydrocarbons, the hydrocarbon reactive polymer 504 expandsoutwardly since the underlying layer is a low loss, low dielectricnon-compressible material 506. The forces created by the expansion orswelling of the hydrocarbon reactive polymer 504 are transferred to theconductive sheath 503 and the expandable, permeable conductive cover502, which causes both the conductive sheath 503 and the expandable,permeable conductive cover 502 to move in an outward direction away fromthe center conductor 508. The low loss, low dielectric non-compressiblematerial 506 may be similar to the low loss, low dielectricnon-compressible material 306, described with respect to FIG. 3 . Thecenter conductor 508 may comprise any conductive material capable oftransmitting electrical signals.

When the hydrocarbon reactive polymer 504 of FIG. 5 expands, it causesthe conductive sheath 503 and the expandable, permeable conductive cover502, when present, to move in an outward direction and create a greaterdistance between the conductive sheath 503 and the center conductor 508.Since the conductive sheath 503 and the expandable, permeable conductivecover 502 are moved farther away from the center conductor 508, theimpedance of the hydrocarbon leak detection cable 500 changes at thatlocation. A change in the impedance at that location, where thehydrocarbon has caused the hydrocarbon reactive polymer 504 to swell orexpand, causes a reflection of an interrogation pulse from a time domainreflectometer. In that manner, the location of the hydrocarbon leak canbe determined, as described above. Both the expandable, permeableconductive cover 502, when present, and the conductive sheath 503provide conduction along the length of the hydrocarbon leak detectioncable 500 so that multiple leaks can be detected along the length of thehydrocarbon leak detection cable 500.

FIG. 6 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable 500 illustrated in FIG. 5 . As illustrated in FIG.6 , the expandable, permeable conductive cover 502 allows hydrocarbonsto permeate the expandable, permeable conductive cover 502 and providesa protective cover for the hydrocarbon leak detection cable 500. Theexpandable, permeable conductive cover 502 is capable of expanding andhas sufficient elasticity to allow the expandable, permeable conductivecover 502 to return to its original size. Hydrocarbons that penetratethe expandable, permeable conductive cover 502 contact the conductivesheath 503. Conductive sheath 503 is also permeable to hydrocarbons andallows the hydrocarbons to pass through the conductive sheath 503 to thehydrocarbon reactive polymer 504. Again, conductive sheath 503 maycomprise an expandable material that has sufficient elasticity to returnto its original size and shape and allow hydrocarbons to pass throughthe conductive sheath 503 to the hydrocarbon reactive polymer 504. Theconductive sheath 503 may be a conductive elastic tape with perforationsto allow the hydrocarbons to pass through the conductive sheath 503, anelastic conductive mesh, or an elastic material covered with aconductive coating or other similar material. Conductive sheath 503 mayalso be made from a polymer that is porous to hydrocarbons and infusedwith conductive particles to be conductive. The conductive sheath 503can be made from a polymer that is sufficiently resistant to wear thatthe expandable, permeable conductive cover 502 can be eliminated. Lowloss, low dielectric non-compressible layer 506 surrounds the centerconductor 508. Since the low loss, low dielectric non-compressible layer506 does not compress, forces created by the expansion of thehydrocarbon reactive polymer 504 are directed outwardly to expand theconductive sheath 503 in an outward direction and increase the distancebetween the conductive sheath 503 and the center conductor 508. Thiscauses a change in the impedance of the hydrocarbon leak detection cable500 which can be detected by a time domain reflectometer.

FIG. 7 is an embodiment of a hydrocarbon leak detection optical fiber700. As illustrated in FIG. 7 , hydrocarbon leak detection optical fiber700 has a permeable cover 702 that protects the hydrocarbon leakdetection optical fiber 700 from abrasion, wear, and punctures, and ispermeable to hydrocarbons. Various silicon permeable membrane materialscan be utilized as a hydrocarbon permeable membrane. This is more fullydisclosed in a paper entitled “Membranes for Hydrocarbon FueledProcessing and Separation” by A. Gugliuzza, A. Basile that appears inAdvanced Membranes Science and Technology For Sustainable Energy andEnvironmental Applications, 2011. Silicone rubber also has permeabilitycharacteristics to hydrocarbon as disclosed in the Society for theAdvancement of Material and Process Engineering, Fall TechnicalConference 2006 “Global Advances and Materials in Process Engineering”proceedings, Coatings and Sealants Section, Nov. 6, 2006 Dallas Texas ina paper entitled “The Permeability Characteristics of Silicone Rubber”by Haibing Zhang PHD, Andy Cloud Arlon Silicone Technologies Division,1100 Governor Lea Road, Bear, Delaware 19701. As such, various membranesexist that are permeable to hydrocarbons including silicone rubber andvarious rubber materials, as disclosed above.

The fiber optic filament 706 of FIG. 7 is surrounded by cladding 704 tocreate the optical portion of the hydrocarbon leak detection opticalfiber 700. The interface between the cladding 704 and the fiber opticfilament 706 creates a reflective surface which causes light to bereflected and transmitted through the fiber optic filament 706. Cladding704 may be made from a hydrocarbon reactive material such as acrylicthat can swell to compress the fiber optic filament 706 and create areflection in the optical signals that are being transmitted through thefiber optic filament 706. Alternatively, cladding 704 can interrupt thereflective interface between the cladding 704 and the fiber opticfilament 706 such as by changing the reflectivity of the interfacebetween the cladding 704 and fiber optic filament 706 by changing itsstructure or color. Light signals passing through the fiber opticfilament 706 will then be scattered and will be reflected back to thesource. Reflected waves can be detected and the length of time betweenthe emission of an optical signal and the return of a reflected wave canbe measured to determine the location of a leak on the hydrocarbon leakdetection optical fiber 700. As such, scattered light that is reflectedat the location of the leak creates an indication of the location of thehydrocarbon leak. The permeable cover 702 can either be expanding ornon-expanding. Cladding 704 may swell and if the permeable cover 702 isexpandable, a disruption of the optical interface between the cladding704 and the fiber optic filament 706 may be created. In anotherembodiment, if the cladding 704 is hydrocarbon permeable, hydrocarbonliquid can seep through the cladding 704 to interrupt the reflectiveinterface between the cladding 704 and the fiber optic filament 706 tochange the reflectivity of the hydrocarbon leak detection optical fiber700 and create scattered light.

FIG. 8 is a cross-sectional view of the hydrocarbon leak detectionoptical fiber 700 illustrated in FIG. 7 . As illustrated in FIG. 8 , thepermeable cover 702, which can be expanding, or non-expanding, surroundsthe cladding 704 that swells or changes color. Fiber optic filament 706is surrounded by the cladding 704.

FIG. 9 is a cut-away view of another embodiment of a hydrocarbon leakdetection cable 900. As illustrated in FIG. 9 , a hydrocarbon permeablecover 902 surrounds a hydrocarbon permeable conductive sheath 903. Ahydrocarbon permeable membrane 904 is also permeable to hydrocarbonswhich allows hydrocarbons to penetrate the hydrocarbon permeablemembrane 904. Hydrocarbon permeable materials such as silicone rubberand other rubbery materials, as disclosed in the papers cited withrespect to the description of FIG. 7 , can be utilized here for thehydrocarbon permeable cover 902, the hydrocarbon permeable conductivesheath 903 and the hydrocarbon permeable membrane 904. A shaped, lowloss, dielectric material 906 is disposed between the hydrocarbonpermeable membrane 904 and the center conductor 908. Liquid hydrocarbonsthat permeate the hydrocarbon permeable cover 902, the hydrocarbonpermeable conductive sheath 903 and the hydrocarbon permeable membrane904, fill the openings or spaces around the shaped, low loss, dielectricmaterial 906. The hydrocarbons disposed within the spaces adjacent tothe shaped, low loss, dielectric material 906, cause a change inimpedance between the center conductor 908 and the hydrocarbon permeableconductive sheath 903, which can be detected by a time domainreflectometer. Again, the hydrocarbon permeable cover 902 can beeliminated if hydrocarbon permeable conductive sheath 903 is madesufficiently rugged to resist wear.

FIG. 10 is a cross-sectional view of the embodiment of the hydrocarbonleak detection cable 900, illustrated in FIG. 9 . As illustrated in FIG.10 , the hydrocarbon permeable cover 902 allows hydrocarbons to passthrough to hydrocarbon permeable conductive sheath 903. Hydrocarbonpermeable conductive sheath 903 also allows the hydrocarbons to permeatethe hydrocarbon permeable conductive sheath 903 to the hydrocarbonpermeable membrane 904. Hydrocarbons then enter the openings or spaces910, 912 to create a change in impedance of the hydrocarbon leakdetection cable 900. Openings or spaces 910 and 912 are created by theshape of the shaped dielectric 906. A change in impedance can bedetected between the center conductor 908 and the hydrocarbon permeableconductive sheath 903 as a result of the hydrocarbon liquid deposited inopenings or spaces 910, 912.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andother modifications and variations may be possible in light of the aboveteachings. The embodiment was chosen and described in order to bestexplain the principles of the invention and its practical application tothereby enable others skilled in the art to best utilize the inventionin various embodiments and various modifications as are suited to theparticular use contemplated. It is intended that the appended claims beconstrued to include other alternative embodiments of the inventionexcept insofar as limited by the prior art.

What is claimed is:
 1. A method of detecting hydrocarbon leaks using ahydrocarbon leak detection cable comprising: providing a hydrocarbonleak detection cable having a hydrocarbon reactive polymer that expandsin the presence of hydrocarbons and generates forces that move aconductive sheath closer to a center conductor of said hydrocarbon leakdetection cable which changes impedance of said hydrocarbon leakdetection cable at a location where said hydrocarbons are contactingsaid hydrocarbon leak detection cable; using a time domain reflectometerto detect said location on said hydrocarbon leak detection cable.
 2. Ahydrocarbon leak detection cable comprising: a center conductor thattransmits an interrogation pulse through said hydrocarbon leak detectioncable; a dielectric material surrounding said center conductor, ahydrocarbon reactive polymer having conductive particles dispersedthroughout said hydrocarbon reactive polymer to cause said hydrocarbonreactive polymer to be conductive and provide a conductive shield forsaid hydrocarbon leak detection cable, said hydrocarbon reactive polymerexpanding in the presence of hydrocarbons which causes said conductiveparticles to move away from each other and reduce conductivity of saidhydrocarbon reactive polymer where said hydrocarbon leak detection cablehas expanded.
 3. The hydrocarbon leak detection cable of claim 2 furthercomprising: an expandable, permeable cover that surrounds saidhydrocarbon reactive polymer that is permeable to hydrocarbons andexpands in response to expansion of said hydrocarbon reactive polymer.4. The hydrocarbon leak detection cable of claim 2 wherein saiddielectric material in non-compressible.
 5. A method of detecting alocation of a hydrocarbon leak in a hydrocarbon leak detection cablecomprising: using a layer of hydrocarbon reactive polymer that functionsas an electrical shield in said hydrocarbon leak detection cable, andthat surrounds a center conductor at a predetermined distance whichcreates a predetermined input impedance of said hydrocarbon leakdetection cable, said hydrocarbon reactive polymer having conductiveparticles dispersed in said hydrocarbon reactive polymer which causessaid hydrocarbon reactive polymer to be conductive and function as anelectrical shield; detecting a hydrocarbon leak at said location on saidhydrocarbon leak detection cable by allowing liquid hydrocarbon fromsaid hydrocarbon leak to penetrate said hydrocarbon leak detection cableat said location causing said hydrocarbon reactive polymer to absorbsaid liquid hydrocarbon, which causes said hydrocarbon reactive polymerto swell so that said conductive particles move away from each otherthereby reducing conductivity of said layer of hydrocarbon reactivepolymer and causing said hydrocarbon leak detection cable to changeimpedance at said location; using a time domain reflectometer todetermine where on said hydrocarbon leak detection cable said change ofimpedance has occurred to determine said location of said hydrocarbonleak.
 6. A hydrocarbon leak detection cable comprising: a centerconductor that is conductive to electrical signals; a dielectricmaterial surrounding said center conductor; a hydrocarbon reactivelayer, disposed over said non-compressible dielectric material, saidthat expands in the presence of hydrocarbons; an expandable conductivesheath, that is permeable to liquid hydrocarbons, disposed over saidhydrocarbon reactive material which provides a conductive shield forsaid center conductor that is spaced apart from said center conductor byan amount that creates a predetermined input impedance of saidhydrocarbon leak detection cable.
 7. The hydrocarbon leak detectioncable of claim 6 further comprising: an expandable covering disposed onsaid conductive sheath that is permeable to said liquid hydrocarbonsthat allows said liquid hydrocarbons to penetrate said expandablecovering and said expandable conductive sheath so that said hydrocarbonreactive layer absorbs said liquid hydrocarbons and expands, whichpushes said expandable conductive sheath away from said center conductorcausing a change in impedance at a location where said hydrocarbonreactive layer absorbs said liquid hydrocarbons.
 8. The hydrocarbon leakdetection cable of claim 6 wherein said dielectric material isnon-compressible.
 9. A method of detecting a hydrocarbon leakcomprising: providing a hydrocarbon leak detection cable having ahydrocarbon reactive polymer that expands when placed in contact withliquid hydrocarbons and generates forces that move a conductive sheathaway from a center conductor in said hydrocarbon leak detection cable,causing a change in impedance of said hydrocarbon leak detection cableat a location where said liquid hydrocarbons contact said hydrocarbonleak detection cable; using a time domain reflectometer to detect saidlocation on said hydrocarbon leak detection cable.
 10. A hydrocarbonleak detection optical fiber comprising: a fiber optic filament thattransmits light; a hydrocarbon reactive polymer covering said fiberoptic filament that creates a reflective interface with said fiber opticfilament that is altered when liquid hydrocarbons contact saidhydrocarbon reactive polymer causing light scattering; a hydrocarbonpermeable cover over said hydrocarbon reactive polymer that allowshydrocarbons to contact said hydrocarbon reactive polymer.
 11. A methodof detecting a hydrocarbon leak comprising: providing a hydrocarbon leakdetection optical cable having a hydrocarbon reactive polymer thatcreates a reflective interface with a fiber optic filament to reflectlight that is transmitted through said fiber optic filament, saidreflective interface being altered when liquid hydrocarbons contact saidhydrocarbon reactive polymer, causing said reflective interface toscatter light; detecting said scattered light to determine a location ofsaid hydrocarbon leak.
 12. A hydrocarbon leak detection optical fibercomprising: a fiber optic filament that transmits light; a hydrocarbonpermeable cladding covering said fiber optic filament that creates areflective interface with said fiber optic filament that is altered whenliquid hydrocarbons permeate said permeable cladding and contact saidreflective interface causing light scattering; a hydrocarbon permeablecover over said hydrocarbon permeable cladding that allows hydrocarbonsto pass through said hydrocarbon permeable cover to said hydrocarbonpermeable cladding.
 13. A method of detecting a hydrocarbon leakcomprising: providing a hydrocarbon leak detection optical cable havinga hydrocarbon permeable cladding that creates a reflective interfacewith a fiber optic filament to reflect light that is transmitted throughsaid fiber optic filament, said reflective interface being altered whenliquid hydrocarbons contact said reflective interface, causing saidreflective interface to scatter light; detecting said scattered light todetermine a location of said hydrocarbon leak.
 14. A hydrocarbon leakdetection cable comprising: a center conductor that conducts electricalsignals; a shaped dielectric material disposed over said centerconductor; a hydrocarbon permeable membrane disposed over said shapeddielectric material so that spaces are present between said shapeddielectric material and said hydrocarbon permeable layer; a hydrocarbonpermeable conductive sheath disposed over said hydrocarbon permeablemembrane that provides a conductive shield for said center conductor andcreates a predetermined input impedance of said hydrocarbon leakdetection cable, said hydrocarbon permeable conductive sheath beingpermeable to liquid hydrocarbons from a hydrocarbon leak so that saidliquid hydrocarbons contacting said hydrocarbon permeable conductivesheath pass through said hydrocarbon permeable conductive sheath andsaid hydrocarbon permeable membrane and are deposited in said spaceswhich changes impedance of said hydrocarbon leak detection cable at alocation where said liquid hydrocarbons from said hydrocarbon leak arelocated.
 15. The hydrocarbon leak detection cable of claim 14 furthercomprising: a hydrocarbon permeable cover that surrounds saidhydrocarbon permeable conductive sheath that is permeable tohydrocarbons.
 16. A method of detecting a hydrocarbon leak comprising:providing a hydrocarbon leak detection cable having a shaped dielectricthat covers a center conductor, and a hydrocarbon permeable membranethat covers said shaped dielectric and forms spaces between said shapeddielectric and said hydrocarbon permeable membrane, and a hydrocarbonpermeable conductive sheath that covers said hydrocarbon permeablemembrane which provides a conductive shield for said center conductorwhich creates a predetermined input impedance of said hydrocarbon leakdetection cable, said hydrocarbon permeable membrane and saidhydrocarbon permeable conductive sheath allowing liquid hydrocarbonsfrom a hydrocarbon leak to penetrate said hydrocarbon permeable membraneand said hydrocarbon permeable conductive sheath and collect in saidspaces between said shaped dielectric and said hydrocarbon permeablemembrane which changes impedance of said hydrocarbon leak detectioncable at a location where said liquid hydrocarbons penetrate saidhydrocarbon permeable membrane and said hydrocarbon permeable conductivesheath; using a time domain reflectometer to detect said location.